Hidden in plain sight: a new Cuscuta species from southwest Utah and northwest Arizona (section Californicae, subgenus Grammica, Convolvulaceae)

Cuscuta nuwuviana, a new species from southwest Utah and northwest Arizona is described and illustrated. The phylogenetic analyses revealed that the new species belongs to a subclade of sect. Californicae (subg. Grammica) that also includes C. draconella and C. decipiens. Although not statistically significant, a topological incongruence between the plastid and nuclear data suggests that C. draconella most likely resulted from the homoploid hybridization of C. nuwuviana and C. decipiens, accompanied by plastid introgression.  Optical and scanning electron microscopy were employed to morphologically distinguish C. nuwuviana from C. draconella and C. decipiens, and an identification key was provided. Field investigations allowed the description of the habitat and plant community of the new species, which is currently known from only two populations in which it parasitizes solely Gutierrezia microcephala (Asteraceae). Evolutionary relationships, infrastaminal scales, and the presence of floral stomatiferous protuberances in sect. Californicae are discussed.